By Alex Jensen

SEOUL

North Korea accused South Korea on Sunday of pursuing an "ulterior intention" by investigating alleged pro-North links behind knife attack on US Ambassador Mark Lippert in Seoul.

Kim Ki-jong, 55, was formally arrested Friday on multiples charges, including attempted murder, after being caught red-handed wounding Lippert's face and arm during a breakfast event the day before.

Kim made it clear to onlookers that he was unhappy about ongoing joint South Korean-American military drills, and about Lippert's role in inter-Korean relations since the 42-year-old only took up his post in Seoul last year.

South Korean authorities have also been trying to establish whether there might be a more concrete link to North Korea, which has repeatedly condemned the allies' joint military exercises. Seoul police have confiscated more than 20 books and materials from Kim's office and home, according to local news agency Yonhap.

Kim has previously made multiple authorized trips north of the heavily guarded inter-Korean border and even tried to set up an alter in memory of late North Korean leader Kim Jong-un upon his death in 2011.

While investigators look into a possible breach of South Korea's strict National Security Law, Pyongyang has been defiant.

Having already described the attack on Lippert as a "deserved punishment," North Korea claimed Sunday that South Korea was making "a desperate attempt to link the case with North Korea."

"The South Korean regime's ulterior intention is to egg its American master on to re-list [North Korea] as a 'sponsor of terrorism' and strengthen the collusion with the U.S.," read the statement from the North's Committee for the Peaceful Reunification of Korea.

Meanwhile, Lippert could be set for an earlier release from Seoul's Severance Hospital than Wednesday, the original date put forward by doctors treating him.

The envoy, having undergone 80 stitches, could be discharged Tuesday afternoon, according to a briefing delivered to reporters Sunday.